Since 1978, a longitudinal study investigating the effects of marihuana and cigarettes used during pregnancy has been underway. The overall purpose of this Ottawa Prenatal Prospective Study is to examine the effects of these drugs on pregnancy, the neonate and the young child. The general objective of the proposed work is to determine whether particular developmental delays and behavioural difficulties observed in the newborn and infant that are statistically associated with prenatal marihuana and cigarette exposure persist in the 4-6 year old child. Among the marihuana offspring particular attention will be paid to visual functioning, body state alterations and fine motor abilities as these were noted to be altered in the infant. Among the offspring of cigarettes users particular attention will be paid to auditory functioning, motor development and attentional behaviour- all of which were related in infancy to in utero cigarette exposure. The battery at 4 years of age will include an assessment of cognitive performance, motor skills and verbal abilities. At 5 and 6 years of age the battery will include an examination of fine and gross motor abilities, sensory skills (tactile visual and auditory), kinesthetic functioning, visual-spatial capabilities, language skills, reasoning ability, memory (visual, tactile and language), intelligence, academic readiness, phonemic awareness and overall behaviour. Maternal variables (e.g., health, nutrition, parity, age, other drugs) and post-natal variables (e.g. home environment, second-hand smoke, preschool) will be included in multivariate statistical analyses. The Ottawa study is the only work to follow-up marihuana offspring beyond a year of age and is the most comprehensive, longitudinal work examining 4-6 year old children of cigarette smokers. The testing of children of this age is particularly critical as the prediction of subtle learning difficulties is most likely to come from studies of this age group.